Venetian blinds of the type that have freely suspended slats without side guides may be manufactured to precise measurements, i.e. with a pre-defined slat length and height of the Venetian blind, or else only the width and slat length are pre-defined by the width of a window, and the height of the Venetian blind must then be adjusted on location, so that the Venetian blind may be adjusted during use without any part rubbing against the window sill or the similar. A Venetian blind consists of a number of ladder cords that carry and adjust the angle of the slats, and raising cords or draw cords that pass through cut-outs in the slats and are fastened to the bottom rail. The adjustment of the angle is usually carried out by lifting one part of the ladder while lowering the other, and raising occurs by lifting the bottom rail by means of the raising cords, so that one slat after the other comes to rest on a pack of slats that increases in thickness. The bottom rail must have a certain stiffness so that the pack of slats may remain flat and not sag between the points of attachment of the raising cords. The ladder cords may either be adjusted by means of an operation that is separate from the raising function or else it is performed by reversing the direction of rotation of the same actuating device that also performs the raising. In the last instance the raising cords are wound around drums in the top rail.
The strings have to be fastened securely to the bottom rail, and various methods to obtain this are known, comprising threading them through holes that are provided for the purpose. A known solution uses holes in the upper side of a hollow bottom rail, through which the strings are threaded, whereupon a knot is tied or a lock is provided on the inside. This bottom rail is split lengthwise in two, and during the assembly the ladders are pinched at the outer edges. Thereby the bottom rail is made into a hollow profile with the desired stiffness. However, this solution suffers from the disadvantage that the adjustment is changed by the very clipping together of the two parts of the bottom rail.